A gas turbine is composed of a compressor, a combustor, and a turbine. The compressor compresses air taken in through an air inlet to produce high-temperature, high-pressure compressed air. The combustor supplies fuel to the compressed air and combusts the mixture to produce high-temperature, high-pressure combustion gas. The turbine has a plurality of turbine vanes and turbine blades alternately installed in a passage inside a casing, and drives a rotor (rotating shaft) coupled to a generator to rotate as the turbine blades are driven by the combustion gas supplied to the passage. The combustion gas having driven the turbine is discharged as exhaust gas from an exhaust chamber into the atmosphere.
In the related art, for example, the gas turbine described in Patent Literature 1 shows a cooling structure of an exhaust chamber. The exhaust chamber is disposed, relative to the last-stage turbine blades of the gas turbine, on the downstream side in the combustion gas flow direction and the axial direction of the rotating shaft, and includes a casing wall and struts. The casing wall has a cylindrical shape so as to form the external shape of the exhaust chamber. The plurality of struts are disposed in the circumferential direction on the radially inner side of the casing wall, and connected to a bearing cover that houses a bearing supporting the rotating shaft. The exhaust chamber is further provided with a cylindrical outer diffuser disposed on the radially inner side of the casing wall, and a cylindrical inner diffuser disposed on the radially outer side of the bearing cover. The inlet of the outer diffuser that is located on the axially upstream side in the combustion gas flow direction is disposed so as to face the last-stage turbine blades. The inlet of the inner diffuser that is located on the axially upstream side is disposed so as to face the base ends (blade roots) of the last-stage turbine blades. The outer diffuser and the inner diffuser are penetrated by the struts, and the corresponding through-holes of the diffusers are connected to each other through strut covers that cover the outer peripheries of the struts.